Without knowing the size of your steam shower area, it is difficult to say. Typically, in small enclosures, a folding seat is preferable so that it can be folded out of the way when not in use. However, nothing beats having a bench where you can lie down!

You can use the same materials for the bench that you use on the walls. Ideally your bench top will be a sold surface since it's not very comfortable to sit on grout lines. Or use larger tiles.Side note: Floor tiles work best with more grout lines, like 2"x2" to allow for better traction.